This invention relates to the use of zinc octoates as hydrogen sulfide scavengers. Petroleum asphalt is produced as a residue of a thermal separation refinery process. The thermal separation process causes thermal cracking to occur which frequently causes hydrogen sulfide to be present in the asphalt stream. In fact, thermal cracking continues in the asphalt even after the asphalt has left the vacuum distillation section of the operation, particularly at high temperature. In order to permit the safe loading, handling, and storage of the asphalt, it is necessary to reduce the hydrogen sulfide to safe levels in the asphalt. This has been done in the past by weathering of the hot asphalt for sufficient time for the hydrogen sulfide to be reduced to safe levels. This not only takes a considerable amount of time (several days), but it releases hydrogen sulfide to the vapor space in the storage, which could create hazardous conditions. Moreover, recent emphasis on environmental regulations in Europe stresses the limits on the hydrogen sulfide content of vent gas.
Other efforts to avoid these problems involve operating the vacuum distillation tower at a lower temperature to reduce thermal cracking in the residue. Lower temperature operation is achieved by increasing the flow of asphalt in a quench loop. This, however, is less efficient than operating at higher temperatures and decreases throughput and thermal recovery. Other related methods of addressing this situation are described in European Patent Specification, Publication No. 0121377 and European Patent 000 421 683 A1.
U.S. Pat. No. 5,000,835 describes using metal carboxylates as hydrogen scavengers. This patent describes the reaction between metal carboxylates with 6 to 24 carbon atoms. In these metal carboxylates, the carbonyl group functions as a carrier for the oppositely charged metal and places the metal into a form which is soluble in an organic environment and able to make contact with dissolved hydrogen sulfide. When the metal in the metal carboxylates reacts with dissolved hydrogen sulfide, the two form insoluble metal sulfides, which eliminate the toxic and corrosive properties of the hydrogen sulfide. While this patent does mention the use of zinc octoate, which is oil soluble and readily available it also notes that zinc octoate is less effective than other metal carboxylates.
Thus there is clear need and utility for an improved method of using zinc octoate as a hydrogen sulfide scavenger. The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists.